regular arrival of a Seaboard and Western CL44 freighter (based on the 'whispering giant' Britannia)
Yes indeed, but with RR Tyne engines. Occasionally we plane spotters living in Isleworth noted strange behaviour of these aircraft when LHR were on easterlies - soon after take-off the engine noise would momentarily reduce significantly for a few seconds and then increase back to climb power.
When I joined the BEA Vanguard fleet some years later we learned that the BEA SOP had been similar, except that the power reduction was done at top of climb - something to do with 'offloading the splines' or some such. By the time we converted onto the type the problem had been solved and the SOP discontinued.